1. Field of the Invention
The present invention relates to a hybrid battery and its charging/discharging method, and more specifically, the present invention relates to automatically charging/discharging batteries having different capacities.
2. Description of the Related Art
Recently, compact and lightened portable electrical/electronic devices have been quickly developed and produced, including cellular phones, notebook computers, camcorders, etc. Accordingly, the portable electrical/electronic devices have built-in battery packs in order that they may be operated in a place where a separate power source is not supplied. The battery packs recently employ batteries which may be charged and discharged simultaneously, taking economy into consideration. Such batteries typically include Ni—Cd batteries, Ni-MH batteries, Li batteries and Li-ion secondary batteries. An operational voltage of a Li-ion secondary battery is three times as high as that of a Ni—Cd battery or an Ni-MH battery which is usually used as a power source of portable electronic devices. Furthermore, Li-ion secondary batteries are widely used since they have a high energy density per unit weight.
Such a Li-ion secondary battery uses a Lithium-based oxide as a positive electrode active material and a carbon material as a negative electrode active material. Generally, a battery type is divided into a liquid electrolyte battery and a polymer electrolyte battery according to the electrolyte type, where a battery using the liquid electrolyte is called a Li-ion battery and a battery using the polymer electrolyte is called a Lithium polymer battery. Furthermore, lithium secondary batteries are manufactured in different types, representatively including a cylindrical type, a square type and a pouch type.
A battery of such shapes is connected to a protection circuit, which is used to select charging or discharging of the battery or to cut off power when the battery is overcharged or when excessive current flows through the battery, thus protecting the battery. One or a plurality of batteries along with the protection circuit is connected in series or in parallel with portable electronics. When the battery is used in portable electronics consuming a large amount of power, such as a notebook computer, generally a plurality of cylindrical type batteries are connected in series and in parallel, thus increasing the running time and power output of battery.
The plurality of cylindrical type batteries mounted in the thin portable electronics, such as a notebook computer, each have the same capacity and size. When the cylindrical type batteries of the same size are mounted in the portable electronics, for example, a notebook computer, there may be formed a space in the notebook computer. When the pouch type battery is mounted in the space, the capacity of the battery may be increased.
However, the pouch type batteries connected to the cylindrical type batteries may have different capacities thereof. If, a protection circuit controls charging/discharging of batteries having different capacities, some batteries whose charging schemes are different to that of the protection circuit may cause non-uniform charging or non-uniform discharging, including over-discharging.
In addition to non-uniform charging/discharging, there are problems of automatically charging/discharging batteries having different capacities, and controlling short and abnormal operation of such batteries.